But what was surprising is that the effect of coffee and napping varied by age. For middle-aged drivers, aged 40 to 50, coffee was a far better choice. Caffeinated coffee lowered risk for these drivers by 89 percent, while the nap only reduced line crossings by 23 percent. But among younger drivers, a nap was almost as effective as caffeine. Among 20- to 25-year-old drivers, the risk of line-crossing fell by 66 percent after a nap, and 74 percent after drinking caffeinated coffee.